1. Field of the Invention
This invention relates generally to systems for verifying quality control, and more particularly, to a system that ensures that a part or assembly is pressed to depth within a predetermined tolerance and measurement accuracy, and that determines the quality of the interference fit.
2. Description of the Related Art
In current pressing applications it is difficult or impossible to determine whether a pressed-in part has been pressed to a fully seated condition when the operation is complete. Current systems endeavor to ensure that a pressed-in part is fully seated by monitoring the press force and continuing the operation until a predetermined amount of force is applied. This predetermined amount of force is assumed to insure that the pressed part is driven to a full seating position, and that the force applied is representative of the quality of the interference fit. These assumptions, however, are not always correct. The force required to overcome the interference fit in the pressing operation oftentimes exceeds the preset force limit of this known approach. Sometimes, a particle of dirt or metal will become lodged behind the part that is being pressed, causing a false reading on the press force. Thus, the application of the full measure of the predetermined force will not always result in complete inward displacement and seating of the part desired to be pressed into place.
A second current method of verifying press quality is to measure the depth of press at the press ram head. Unfortunately due to part and casting variations this simple single-measurement system is inadequate, as it will not identify the quality of a precision pressing operation.
In the case of a valve seat in an engine head, or a bearing cup in an assembly, the normal working forces, vibration, and heat of the product will finally seat the incorrectly assembled part during the engine or component""s normal working life. This form of seating action, however, will generally cause changes in the running clearances of the assembly that are critical to the product""s over all life or performance.
In addition to the foregoing, valve seats in particular are subjected to tremendous amounts of heat from exhaust gasses. Oftentimes, the temperature of the exhaust gas approaches the melting point of some metals. It is essential that proper seating of the valve seat within the receiving pocket be effected to promote transference of the heat to the cylinder head casting, which contains the cooling water jackets.
There is a need, therefore, for a quality monitoring system that overcomes the foregoing problems.
It is, therefore, an object of this invention to provide a system for pressing-in a press-fit part, such as a valve seat or bearing cup, into a receiving pocket in a receiving assembly, such as a cylinder head, that achieves seating of the part to a predetermined depth reliably.
It is another object of this invention to provide a system for pressing-in a press-fit part to achieve seating within predetermined tolerances without applying excessive continuous insertion force.
It is also an object of this invention to provide a self-aligning press fit ram.
It is a further object of this invention to provide a system for pressing-in a press-fit part to achieve verified seating within predetermined tolerances.
It is additionally an object of this invention to provide a system for pressing-in a press-fit part, such as a valve seat or bearing cup, into a receiving pocket in a receiving assembly, such as a cylinder head, that achieves seating of the part to a predetermined depth reliably, notwithstanding variations in dimensions of the press-fit part.
It is yet a further object of this invention to provide a system for pressing-in a press-fit part, such as a valve seat or bearing cup, into a receiving pocket in a receiving assembly, such as a cylinder head, that achieves seating of the part to a predetermined depth reliably, notwithstanding variations in depth of the receiving pocket.
It is also another object of this invention to provide a system for pressing-in a press-fit part into a receiving pocket in a receiving assembly wherein the insertion force is monitored.
The invention will be shown in one embodiment to be applied to pressing valve seats for an engine head. Bearing cups or any other precision pressing operation could use the same technology.
The foregoing and other objects are achieved by this invention which provides, in accordance with a first method aspect thereof, a method of verifying the quality of a pressing operation of a press-fit part onto a receiving portion of a receiving assembly. The method includes the steps of:
first measuring a predetermined dimension of the press-fit part to establish a first measurement value;
directing a first measuring probe to the receiving portion of the receiving assembly onto which the press-fit part is to be pressed;
second measuring the receiving portion of the receiving assembly onto which the press-fit part is to be pressed, to establish a second measurement value;
urging the press-fit part onto the receiving portion of the receiving assembly;
third measuring a portion of the receiving portion of the receiving assembly that extends beyond a predetermined surface of the press-fit part to establish a third measurement value;
first comparing the third measurement value against the difference between the first and second measurement values to form a first comparison value; and
second comparing the first comparison value against a predetermined comparison value to determine the quality of the pressing operation.
In one embodiment of this method aspect of the invention, the receiving portion of the receiving assembly onto which the press-fit part is to be pressed is a pocket of the receiving assembly. The pocket has a depth that is defined by the distance between outer and inner surfaces thereof Moreover, the step of directing a first measuring probe to a receiving portion of the receiving assembly onto which the press-fit part is to be pressed includes the step of causing the first measuring probe to travel toward and communicate with the inner surface. In a further embodiment, there is further provided the step of second directing a second measuring probe to the outer surface of the pocket of the receiving assembly. The step of second measuring incorporates the step of differential measuring a difference in the respective distances traveled by the first and second measuring probes during the respective steps of first and second directing. Such differential measuring provides an indication of the depth of the pocket of the receiving assembly. In other embodiments, however, where a press-fit part is installed on a shaft, the receiving portion of the shaft is measured in either case, the step of differential measuring incorporates the step of monitoring an electrical signal characteristic provided by a linear variable differential transformer (LVDT), or other measuring device, such as a laser.
In a further embodiment of this first method aspect of the invention, the step of urging the press-fit part into the pocket of the receiving assembly incorporates the further step of translating a ram element in communication with the press-fit part toward the pocket of the receiving assembly. Also, the step of translating a press ram element includes the further step of permitting an angular displacement of the press-fit part with respect to the pocket of the receiving assembly. In this manner, a plane of the press-fit part is made substantially parallel to a plane of the predetermined inner surface of the pocket of the receiving assembly.
In a still further embodiment of this first method aspect of the invention, the step of urging the press-fit part into the pocket of the receiving assembly includes the further step of measuring an insertion force of the press-fit part into the pocket of the receiving assembly to establish an insertion force value over a predetermined insertion distance. This monitoring of force over distance produces an advantageous indication of the quality of the interference fit between the press-fit part and the receiving portion of the receiving assembly. This is enhanced by the step of comparing the insertion force value against a predetermined insertion force value to determine whether the press-fit part is appropriately dimensioned for insertion into the pocket of the receiving assembly.
In a preferred embodiment, the step of urging the press-fit part into the pocket of the receiving assembly includes the further step of measuring an insertion force of the press-fit part into the receiving portion of the receiving assembly to establish an insertion force value over a predetermined insertion distance. The insertion force value is compared against a predetermined insertion force value to determine whether the press-fit part is appropriately dimensioned for insertion into the pocket of the receiving assembly.
In one embodiment, the insertion force is sampled first and second times to produce corresponding first and second insertion force values. These values are correlated to respectively associated installation distances at which the first and second insertion force values were measured. Then a comparison value is produced by comparing the first and second insertion force values. The comparison value, which will have a range of values, is associated with at least one predetermined installation condition. Preferably, a plurality of predetermined installation conditions associated with respective magnitude ranges of the comparison value resulting from said step of comparing. The following are examples:
If the initial and subsequent insertion forces both are below normal, then the press-fit part is too small for the receiving pocket (or too large for the receiving spindle); or
If the initial and subsequent insertion forces both are greater than normal, then either the press-fit part is too large for the receiving pocket (or too small for the receiving spindle); or
If the initial insertion force is normal or greater and the subsequent insertion force is low, then the receiving portion of the receiving assembly is irregularly dimensioned; or
If the initial insertion force is normal and increases significantly, as though the end of the installation travel has been reached, but the installation distance is shorter than a predetermined installation distance, then debris has built up behind the press-fit part, the debris being the result of inadequate pre-installation cleaning or material having been scraped off of the receiving assembly due to the press-fit part being off-center as it is urged onto the receiving assembly.
In a still further embodiment, there is provided the step of continuously sampling the insertion force and the distance over which the insertion force is applied, to form an installation force versus installation distance correlation curve. The correlation curve can provide significant additional information about the quality of the installation of the press-fit part, as well as defects in the machining or preparation of the receiving assembly, which can be reported back to the production line to effect a correction. Such correction can be implemented in-process.
In a still further embodiment, there is provided the further step of applying a supplemental insertion force having a substantially predetermined energy and a short duration. The step of applying a supplemental insertion force includes the further step of accelerating a substantially predetermined mass to impact the press-fit part in the direction of the step of urging. This is performed during the step of urging the press-fit part into the pocket of the receiving assembly. Of course, this step is not limited in its application to the installation of a press-fit part into a pocket, but may be used during installation of a press-fit part onto a shaft.
In still another embodiment of this first method aspect of the invention, after performing the step of second measuring a depth of the pocket of the receiving assembly, and prior to performing the step of urging the press-fit part into the pocket of the receiving assembly, there are provided the steps of:
withdrawing the first measuring probe from the pocket of the receiving assembly; and
installing the press-fit part on a temporary support arrangement.
The press-fit part, in a specific illustrative embodiment of the invention, has an annular configuration. Additionally, the temporary support arrangement includes a finger element about which is installed the press-fit part.
In accordance with a first apparatus aspect of the invention, an arrangement is provided for pressing a press-fit part into a receiving portion of a receiving assembly. In accordance with the invention, a first measuring arrangement measures a predetermined dimension of the press-fit part. A second measuring arrangement measures the receiving portion of the receiving assembly. The press-fit part is urged by a press drive onto the receiving portion of the receiving assembly. Additionally, an impulse drive applies an impetus of short duration to the press-fit part.
In one embodiment of this apparatus aspect of the invention, the receiving portion of the receiving assembly onto which the press-fit part is to be pressed is a pocket of the receiving assembly. There is further provided a holding arrangement for holding the press-fit part in position to be urged into the pocket of the receiving assembly by the press drive. Of course, in some embodiments of the invention, the press-fit part is to be pressed is to be installed on a shaft, as would be the case with a bearing.
There is additionally provided a force measuring arrangement for measuring an insertion force applied to the press-fit part by the press drive. As previously noted, the insertion force can be monitored over a distance of installation of the press-fit part, thereby providing an indication of the quality of the interference fit between the press-fit part and the receiving portion of the receiving assembly.
In a further embodiment of the invention, the second measuring arrangement includes a first probe for communicating with an inner surface of the pocket of the receiving assembly. Additionally, a second probe communicates with an outer surface of the pocket of the receiving assembly. Then, a differential measurement arrangement produces a first electrical measurement signal responsive to a difference in the displacements of the first and second probes. Thus, the depth of the pocket of the receiving assembly is measured.
In a still further embodiment of the invention, there is provided bearing arrangement interposed between the first and second probes. The bearing arrangement includes, in certain embodiments, an interference fit ball or roller bearing arrangement interposed between the first and second probes.
The first probe is arranged, in some embodiments, to communicate with the inner surface of the pocket of the receiving assembly at a plurality of locations thereon. The second probe is arranged to communicate with the outer surface of the pocket of the receiving assembly at a plurality of locations thereon.
An angular displacement arrangement is coupled, in certain embodiments, to the first probe. In this manner, the first probe is angularly displaceable with respect to an axis of translation thereof directed toward the pocket of the receiving assembly and substantially self-aligning with respect thereto. The first and second probes are arranged in certain embodiments of the invention to be axially parallel with respect to each other.
In yet another embodiment of the invention, the press drive is provided with an angular displacement drive that communicates with the press-fit part and renders same to be angularly displaceable with respect to an axis of translation thereof directed toward the pocket of the receiving assembly and substantially self-aligning with respect thereto. The angular displacement of the press drive is responsive to a radius that originates at a distal seating plane of the press-fit part.
In accordance with a further method aspect of the invention, there is provided a method of verifying the quality of a pressing operation of a press-fit part into a pocket of a receiving assembly. The method includes the steps of:
first measuring a predetermined dimension of the press-fit part to establish a first measurement value;
first directing a first measuring probe into the pocket of the receiving assembly;
second directing a second measuring probe onto an outer surface of the receiving assembly;
second measuring a depth of the pocket of the receiving assembly to establish a second measurement value by determining a differential between the steps of first and second directing;
installing the press-fit part on a temporary holding arrangement;
urging the press-fit part into the pocket of the receiving assembly;
third measuring a depth of the pocket to a predetermined surface of the press-fit part to establish a third measurement value;
first comparing the third measurement value against the difference between the first and second measurement values to form a first comparison value; and
second comparing the first comparison value against a predetermined comparison value to determine the quality of the pressing operation.
In one embodiment of this further method aspect of the invention, the step of urging the press-fit part into the pocket of the receiving assembly includes the further steps of
translating a ram element in communication with the press-fit part toward the pocket of the receiving assembly; and
permitting an angular displacement of the ram whereby the press-fit part is self-aligning with respect to the pocket of the receiving assembly.
During performance of the step of urging there is provided the further step of measuring an insertion force of the press-fit part into the pocket of the receiving assembly to establish an insertion force value.
In a further embodiment, there is provided the further step of applying a supplemental insertion force having a substantially predetermined energy and a short duration. This application of a supplemental insertion force incorporates the further step of accelerating a substantially predetermined mass to impact the press-fit part in the direction of the step of urging. Most of the energy supplied to the press-fit part by the impulse of short duration is absorbed by the displacement of the press-fit part in the direction of urging.
In accordance with a further method aspect of the invention, there is provided a method of verifying the quality of a pressing operation of a press-fit part onto a receiving portion of a receiving assembly. The method includes the steps of:
urging the press-fit part by the application of an installation force for a determinable installation distance onto the receiving portion of the receiving assembly;
first measuring a first magnitude of the installation force applied to the press-fit part during said step of urging;
second measuring a first installation distance at which said step of first measuring is performed, the first installation distance being shorter than the determinable installation distance; and
correlating the first force with the first installation distance.
In one embodiment of this further method aspect of the invention, there are provided the steps of:
third measuring a second magnitude of the installation force applied to the press-fit part during said step of urging;
fourth measuring a second installation distance at which said step of third measuring is performed, the second installation distance being shorter than the determinable installation distance;
correlating the second force with the second installation distance; and
comparing the first and second installation forces.
A plurality of installation conditions are associated with respective comparison values that result from the step of comparing. As previously noted, and by way of example, the presence of a non-uniform receiving portion condition is determined in response to a comparison value that corresponds to differences between the first and second installation forces.
In a further embodiment, there are further provided the steps of:
fifth measuring a final installation force applied to the press-fit part during the step of urging, the final installation force being greater than the second magnitude of the installation force; and
sixth measuring a final installation distance, the final installation distance being determined in response to the installation force increasing in magnitude to the magnitude of the final installation force without corresponding progress of the press-fit part onto the receiving assembly.
Of course, the final installation distance is compared to the determinable installation distance to determine whether the press-fit part has been inserted to the necessary extent. A fault condition is issued if the final installation distance IS shorter than the determinable installation distance.
In a highly advantageous embodiment of the invention, there is further provided the step of continuously sampling the installation force and the distance, to form an installation force versus installation distance correlation curve.
As previously noted, the press-fit part is subjected to a supplemental insertion force having a substantially predetermined energy and a short duration. The supplemental insertion force incorporates the further step of accelerating a substantially predetermined mass to impact the press-fit part in the direction of the step of urging. Most of the energy supplied to the press-fit part by the impulse of short duration is absorbed by the displacement of the press-fit part in the direction of urging.
In accordance with a further embodiment of this method aspect the invention, there are further provided the steps of:
first measuring a predetermined dimension of the press-fit part to establish a press-fit part measurement value;
second measuring the receiving portion of the receiving assembly onto which the press-fit part is to be pressed, to establish a receiving portion distance measurement value;
third measuring a portion of the receiving portion of the receiving assembly that extends beyond a predetermined surface of the press-fit part to establish a residual distance measurement value; and
first comparing the residual distance measurement value against a determined difference value corresponding to the difference between the press-fit part and the receiving portion measurement values.